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Assembly and Operating Instructions for HiViz.com Kits

 

Anatomy of a Balloon Shot

 

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Overview

 

Photographing a balloon burst with a projectile is relatively easy to do using a simple sound trigger. Of course, one has to take precautions in firing high-speed projectiles. The method will be discussed in the next section. Here we show some results obtained with a minimal amount of trial and error in adjusting the position of the microphone. Photos 1 and 2 were taken under conditions as nearly identical as possible.They demonstrate the reproducibility possible with the setup. The balloons were shot with an airgun pellet traveling a little under the speed of sound. The view is approximately along the trajectory of the pellet looking in the direction the pellet is traveling. The pellet has just exited the far side of the balloon in both shots, producing a triangular hole. Close examination reveals the pellet just beyond this exit hole. (Click on either image to enlarge.)

 

Water balloon shot with BB (transverse view) Water balloon shot with BB (transverse view)
Photo 1 Photo 2
Both photos were taken with a Nikon D700, 105mm micro lens, f/11, ISO 800, 0.5 microsecond exposure.

 

Primary setup: Photographing the bursting balloon

 

The equipment setup for photographing balloons burst with projectiles is shown in Photo 3 below. (Click on the photo for an even larger version.) Refer to the numbers in the photo in the descriptions to follow.

 

The camera (1), mounted on a tripod, is a Nikon D700 with 105mm micro-Nikkor lens. The camera is positioned for a view nearly parallel to the line of the bullet's path. All manual camera settings are used, and the camera is focused on the knot in the balloon. The shutter is set to be open for 2 seconds, as the flash exposure is taken in a completely-darkened room. The 2 seconds shutter-open time provides time to open the camera shutter and then pull the trigger of the rifle. The rifle (2) is a side-lever cocking, single-shot Diana Model 48 that shoots 4.5mm pellets at nearly the speed of sound.The rifle is mounted on a rest (3) that is clamped to the table to make sure that the rifle remains aimed at the center of the pellet trap (7). The latter, which can barely be seen behind the black paper background (8), is a cardboard cube (about 1 ft on a side) filled with sand. The light source (4) is a 0.5 microsecond spark source built by Prism Science Works. This exposure time is sufficient to freeze the motion of the rip edges.* The balloon (5) is held in place on a post using hook-and-loop tape, one side stuck down to the post and the other to the underside of the balloon. The trigger (6) is the HiViz.com Sound Trigger, model ST2. This simple, piezoelectric trigger is sensitive to the loud sound of the gun firing but not to normal environmental noise, thus avoiding spurious flashes of the SPOT. The switch output of the latter is connected to the ST2 with a long RCA cable. The sound trigger is positioned in order to produce the delay necessary to capture the balloon burst in the desired stage. This is partly a matter of trial and error but can be fine-tuned with small position shifts of the microphone. Moving the trigger toward or away the source of sound changes the time delay by +/- 0.1 millisecond per foot.

 

The SPOT and the ST2 are placed on rolling tables separate from the table holding the rifle and the target. This allows the trigger and flash to be positioned independently for greatest flexibility. The table surfaces are covered with flat black cloth or paper in order to eliminate unwanted reflections. The background is also flat black, although one could choose a different color as desired.

 

A note about white balance when using the SPOT: The spark from this unit produces a bluish light. In order to achieve a natural-looking white balance, a photo was first taken of the flash reflected from an 18% gray card. A white balance preset was then created for the camera using this image. The white balance was further fine-tuned in an editing application.

 

Water balloon shot with BB (transverse view)
Photo 3
This photo shows the setup for taking Photos 1 and 2.

 

*For much less expense than the SPOT, one can substitute a standard photographer's flash unit as the light source. When set at minimum power, such a unit can produce good exposures of ripping balloons with some blur visible in the ripping edges.

 

Secondary setup: Photographing the primary setup in action

 

Photo 3 above shows the entire setup illuminated as the balloon is in the act of bursting. In order to capture this scene at the instant the balloon was bursting, a secondary camera and flash setup was used. This setup is shown below in Photo 4. The secondary camera (1) was a Nikon D200 with 18-55 mm zoom lens set at 18mm. The shutter-open time was set for 2 seconds, the same as the primary camera (1 in Photo 3). In order to control the shutter of the D200 remotely, the shutter cable was connected to the instant shutter output of a Delay Timer (2), and a PocketWizard Plus II transceiver (3). A second transceiver (10 in Photo 3 above) was used by the photographer to open the shutter of the D200 prior to firing the rifle. The secondary flash unit was a Vivitar 283 (4). In order to capture the scene in Photo 3 at the same time as SPOT discharged, a Dual Light Sensor (5) was used to trigger the Vivitar 283. In effect, the Dual Light Sensor controlled the Vivitar 283 as an auxiliary flash unit with SPOT as the main unit. The photosensor (6) that detected the flash of SPOT was positioned in front of SPOT and connected to the Dual Light Sensor with a long cable.

 

Water balloon shot with BB (transverse view)
Photo 4

Procedure

 

In order for one person to control both the primary and secondary setups, the procedure is the following:

  1. Place an inflated balloon on the post.
  2. Pump the rifle and load a pellet in the chamber. Position the rifle on the rest and disable the safety.
  3. Turn out the room lights.
  4. Press the shutter button of the D700 and also the Test button of the transmitting PocketWizard to remotely open the shutter of the D200.
  5. Pull the trigger of the rifle while both shutters are open. The Sound Trigger discharges SPOT and the Dual Light Sensor discharges the Vivitar 283 simultaneously.
  6. Turn on the room lights after both camera shutters close.

 

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